Electronically tunable magnetron



H. K. JENNY 2,759,123

Aug. 14, 1956 INVENTOR. Hams K. JENNY I arrow/5y United States Patent ELECTRONICALLY TUNABLE MAGNETRON Hans K. Jenny, Whippany, N. 3., assignor to Radio 'Corporation of America, a corporation of Delaware Application October 1, 1954, Serial No. 459,731

8 Claims. (Cl. 315-3957) This invention relates to electron discharge devices of the magnetron type, and more particularly to cavity resonator magnetrons which may be electronically tuned or modulated by passing an electron beam thru one or more of the cavity resonators of the magnetron.

It is known to tune or modulate the frequency of oscillation of a cavity resonator magnetron by directing an electron beam thru one cavity resonator in the anode block. This construction is described and shown following pages 592 of volume 6, Microwave Magnetrons of the Radiation Laboratory Series, McGraw-Hill, 1948. The electron beam should be directed thru the resonator at a point where high electric field strength exists in order to maximize the effect of the electron beam. High electric field strength exists near the center of the magnetron where the resonator dimensions are relatively small. It is therefore relatively difficult and expensive to construct a magnetron modulated with an electron beam passing thru the portion of a resonator near the center of the magnetron. The difiiculty is particularly great with strapped magnetrons since the straps are mounted where it is desired to pass the modulating electron beam. Another difiiculty with existing constructions is that when a modulating electron beam is passed thru one resonator of the magnetron, there is a disturbance of the electrical symmetry of the magnetron which puts limitations on the range over which the output frequency of the magnetron can be modulated, and puts limitations on other characteristics of the magnetron.

It is an object of this invention to provide an improved electronically tunable magnetron wherein the modulating electron beam is more effective than has been possible with previous constructions.

It is another object to provide an improved electronically tunable magnetron wherein the modulated electron beam is directed thru all of the resonators of the magnetron so as to preserve perfect electrical symmetry within the magnetron.

It is a further object to provide an improved electronically tunable magnetron which is relatively simple and inexpensive to manufacture by reason of the arrangement wherein the modulating electron beam is directed thru peripheral portions of the resonators.

In one aspect, the invention comprises an electronically tunable magnetron having a central cathode space and a plurality of vanes extending radially therefrom and forming resonator cavities therebetween. The cavities are arranged in pairs with adjacent cavities constituting a pair being in communication with each other at the peripheral ends. The cavities of a pair are separated from each other at the sides by a radially extending vane having a transverse septum on the end thereof spaced from the cylindrical wall of the magnetron. Each pair of coupled cavities forms part of a U-shaped or folded cavity resonator open at its ends to the central cathode space. An annular electron gun directs a cylindrical sheet of electrons thru those portions of the resonators which are 2,759,123 Patented Aug. 14, 1956 between the septa and the outer cylindrical wall of the magnetron.

These and other objects and aspects of the invention Will be apparent to those skilled in the art from the following more detailed description taken in conjunction with the appended drawings, wherein:

Figure 1 is a sectional view taken thru a magnetron constructed according to the teachings of this invention; and

Figure 2 is a sectional view taken on the line Il-II of Figure l.

The electronically tunable magnetron shown in Figures 1 and 2 includes an elongated cylindrical cathode 5 mounted in a cylindrical cathode space 4 at the center of an anode block structure. The anode block structure includes a conductive metallic cylinder 6 having an inner cylindrical wall 7. A first plurality of radial metallic vanes 8 extend radially from the cathode space 4 and are fixed in the block member 6.

A plurality of arcuate metallic partitions or septa 9 are mounted coaxially with and spaced from the cylindrical Wall 7. The septa 9 are in insulated spaced relationship with the radial vanes 8, and all of the septa are joined together by means of an integral metallic annulus 10 located below the vanes S. A second plurality of metallic vanes 11 extends radially from the cathode space 4 with the peripheral ends secured to the centers of respective septa 9. The entire assembly including all of the septa 9, the annulus 1t}, and the second plurality of vanes 11 is supported from a base member 12 of the magnetron by means of a plurality of chokes 13 secured to the bottom edges of the vanes 11. The chokes 13 by virtue of their dimensions serve to electrically isolate the vanes 11 from the base member 12 of the magnetron for radio frequency energy.

It is thus far apparent that the anode block structure provides a plurality of resonator cavities all of which are in communication with each other in the region of the cathode 5. Unlike prior art magnetrons, the peripheral ends of adjacent cavities are in communication with each other in the region between the septa 9 and the wall 7. The adjacent cavities which are in peripheral communication with each other may be considered as being paired. The construction is such that the electrical distance from the cathode space 4, radially out between vanes 8 and 11 forming walls of one cavity, thru the space between the septum 9 and adjacent vane 8, around the septum 9 and back thru the other cavity of the pair to the cathode region 4 is equal to a full-wavelength. The two vanes 8 and intermediate vane 11 forming the sides of each pair of coupled cavities combined with the associated septum 9 and wall 7 form a folded or U-shaped cavity resonator in the form of a folded full-wave section of transmission lineopen at the ends. With this arrangement, the electric field strength is a maximum at the electrical center of each folded resonator, that is, at the center of each area bounded by a septum 9 and the peripheral wall 7. A convenient and effective region is thus provided thru which a modulating electron beam may be passed.

An annular electron gun designated 15 includes an annular cathode, annular accelerating and annular focusing electrodes which direct a cylindrical sheet of electrons downwardly thru the region between the septa 9 and the cylindrical wall 7. The entire magnetron is enclosed within an evacuated envelope constituted by the cylindrical block 6, the base 12, a cup-shaped shielding member 17, polarizing permanent magnet pole pieces 13 and 19 having opposite polarities and seals closing holes 20 and 21 in the pole pieces which in the construction process are used for inserting the cathode 5 and for taking out energizing leads. The energizing leads for the annular electron gun 15 are taken out from the envelope thru a seal designated 22.

v spaced from said vanes, and a second p In the operation of the electronically tunable magnetron of this invent-ion, the magnetron is operated in the usual manner as a generator of radio frequency energy having ,a frequency of oscillation determined by the physical dimensions -and configurations of the anode block. Output energy may be taken from one resonator ofthe magnetron by'means of halo loop and an output coaxial line 24. Halo loop output circuits aredescrihed and illustrated in chapter of"Microwav,e Magnetrons supra. As an alternative to the halo floop output means shown in Figures 1 and 2 of the drawings, the coaxialline 24 maybe taken thru the sidewall of the magnetron. in this case, the annular electron gun 15 may be interrupted at the point where the output coaxial line is connected.

"The "output frequency of the magnetron is modulated at a high rate according to intelligence by modulating the nuniber of electrons directed from the annular electron gun 15 'thru the regionbetween'the septa 9 and the wall 7. According to this invention there is provided an electronically tunable magnetron wherein the modulating electron beam is effective in a partorall of the resonators of the magnetron. Therefore, the output freguenoy of the magnetron is especially responsive to the modulation applied to the electron beam. Further, the construction wherein the modulating electron beam is located at the peripheral part of the anode block is such as to simplify the manufacturing difliculties since the component parts are not so small as required with other constructions, and the manufacturing tolerances are greater.

What is claimed is:

1. An electronically tunable magnetron comprising, a cathode, an anode structure surrounding said eathode and including means forming a plurality of radially extending cavities all in communication with each other in the region of said cathode, said anode structure also including means forming a space communicating with two only of said cavities at the peripheral ends thereof and'forrning with said two cavities a cavity resonator, and means to direct a stream of electrons this said space.

An electronically modulated magnetron comprising, an elongated cathode, an anode structure symmetrical about said cathode and including means forming a pina y of a y e te n t ss a i qminnn cation with each other in the region of said cathode, said anode structure also including vme n o i a space eating with a h P o jacent a it es t the PI s a' sns s and mi i h said Pa s o l9t Y1L p u y o cavity esonat an in an to direc .a cylindrical sheet of electrons thru all of said spaces.

An electronically m dul ssim stl t o f amusin a cathode; an anode structure including, a peripherlal'wall, a iirst plurality of adi l se erts d gi n i e iim i d cathode to said pe iph a al a mo alit of sepia spaced i r ly it m s i ,p ps a wal and in 'li y iradial vanes extending from the region of said cathode to said septa; and means to direct electrons saidspaee between said peripheral wall and said septa.

4. An electronically modulated magnetron as defined in claim 3 wherein said electrons are directed to form a cylindrical sheet of electrons.

5. An electronically tunable magnetron comprising; a cathode; an anode structure including a cylindrical wall, a firstpllt al ty o radia ane e tend ng f om the re i of said cathode to said cylindrical wall, a plurality of arcuate septa spaced inwardly from said cylihdrical wall and spaced from said vanes, a second plurality of radial vanes extend n f om the regio o sa d cat ode o i arcuate septa, and means to direct a cylindrical sheet of electrons thru the space between said cylindrical wall and said septa.

6. An electronically modulated magnetron as defined in claim 5 wherein said anode structure forms a plurality of pairs of resonators, and wherein the electrical distance from the region of the cathode radially outward 'thru one resonator, around the arcuate septum and back the adjacent resonator of the pair to the cathode region constitutes a full-wavelength.

7. An electronically modulated magnetron comprising a cathode, an anode structure symmetrical about said cathode and forming aplurality of pairs of resonators, all the resonators being in communication with each other in the region of said cathode, the resonators of each pair being separated by a radially extending vane having a transverse septum on the end thereof, the resonators of each pair being in communication with each other on the outward-side of said septum, and means to direct a stream of electrons thm said "resonators on the outward side of said septum.

8. An-electronically modulated magnetron comprising: a cathode; an anode structure surrounding said cathode and including aplurality of radial yanes forming radially extending cavities all in communication with each other in the region of said cathode, the radial length of at-least one of said vanes being less than the two adjacent vanes; said anode structure further including a septum extending from the outer end of said one vane toward "but spaced from said two adjacent vanes, and a peripheral wall extending between the outer ends of said'two adjacent vanes, whereby said septum and said peripheral wall form a space communicating with the two cavities formed by said one vane and said two adjacent vanes; and means to direct electrons thru said space between said septum and said peripheral wall.

References Cited in the file of this patent UNITED STATE PATENTS 

